First, I recently built a VMware box, they recommended to have their boot disk be a USB flash drive for that and leave the good drives for VMs. Has anyone tried this with Gentoo, and is it advisable?

Now, beyond that:

I have an SSD and more HDDs than I plan to use.

I'm trying to figure out whether to use LVM2 and make a bunch of virtual growable filesystems, or if I should just make each drive one big partition and then use a bind-style mount to get my partitions on the proper drive type.

Can anyone give advice?

Just so you know what kind of system, I plan to make a developer box with at least two big monitors, with KVM for virtualization. Maybe FVWM. So lots of compiling, some virtualization, and then normal web browsing. Would like to get the TV card working finally.

LVM is the way to go. You can give a each KVM guest, one or more logical volumes for its its filesystem(s) and give the guests raw access to the underlying logical volume. This avoids the overhead of having the guest file systems as files in the hosts filesystem.
You can also grow the logical volume provided to a guest and resize the filesystem.
As the guests see the logical volume as a HDD, you partition it and do a normal install ... almost.
Unless you want to run Windows as a guest, use the virtio drivers, not the emulated hardware.

Be sure to choose a filesystem that supports resizing._________________Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

I already sort of went ahead with something like that. No KVM yet, but LVM2 anyway. I'm pretty familiar with LVM and resizing, the last few installs were just that sort of thing.

I've never done anything serious with KVM before, so I have some reading to do. At least one guest will be Windows, probably 2 of them. If this all works I'll transfer my test licenses over to the KVM box, or maybe KVM can handle a Parallels VM? I guess I'll find out.